fix: Fix setting value to lazy loading ComboBox (#478)

ComboBox should only throw when no items/callback has been set to it.
There is a possibility that the value is set but the backend doesn't have
this item available, but that is an edge case and something that should
not happen and should be possible to prevent by resetting the data and
thus a responsibility of the application developer.

Fixes #391

(cherry picked from commit eb91269)

vaadin-combo-box-flow-parent/vaadin-combo-box-flow/src/main/java/com/vaadin/flow/component/combobox/ComboBox.java

@@ -364,7 +364,8 @@ private static <T> String modelToPresentation(ComboBox<T> comboBox,
 
     @Override
     public void setValue(T value) {
-        if (dataCommunicator == null || dataCommunicator.getItemCount() == 0) {
+        if (dataCommunicator == null || dataCommunicator
+                .getDataProvider() instanceof DataCommunicator.EmptyDataProvider) {
             if (value == null) {
                 return;
             } else {

vaadin-combo-box-flow-parent/vaadin-combo-box-flow/src/test/java/com/vaadin/flow/component/combobox/ComboBoxTest.java

@@ -15,8 +15,6 @@
  */
 package com.vaadin.flow.component.combobox;
 
-import static org.junit.Assert.assertEquals;
-
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -47,6 +45,7 @@
 import com.vaadin.flow.shared.Registration;
 
 import elemental.json.Json;
+import static org.junit.Assert.assertEquals;
 
 public class ComboBoxTest {
 
@@ -307,6 +306,16 @@ public void setValueWithoutItems_throw() {
         combo.setValue("foo");
     }
 
+    // https://github.com/vaadin/vaadin-flow-components/issues/391
+    @Test
+    public void setValueWithLazyItems_doesntThrow() {
+        final ComboBox<String> comboBox = new ComboBox<>();
+        comboBox.setItems(query -> Stream.of("foo", "bar"));
+        comboBox.setValue("foo");
+
+        Assert.assertEquals("foo", comboBox.getValue());
+    }
+
     @Test
     public void clearWithoutItems_doesNotThrow() {
         ComboBox<String> combo = new ComboBox<>();

vaadin-grid-flow-parent/vaadin-grid-flow/src/test/java/com/vaadin/flow/component/grid/GridTest.java

@@ -17,7 +17,9 @@
 package com.vaadin.flow.component.grid;
 
 import java.util.Arrays;
+import java.util.stream.Stream;
 
+import org.junit.Assert;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -51,4 +53,13 @@ public void dataViewForFaultyDataProvider_throwsException() {
         grid.getListDataView();
     }
 
+    @Test
+    public void selectItem_lazyDataSet_selectionWorks() {
+        final Grid<String> grid = new Grid<>();
+        grid.setItems(query -> Stream.of("foo", "bar"));
+        grid.select("foo");
+        Assert.assertEquals(1, grid.getSelectedItems().size());
+        Assert.assertTrue(grid.getSelectedItems().contains("foo"));
+    }
+
 }